Proposed work includes: 1. Efforts to cultivate JC virus in cells other than human fetal glial cells. 2. Continued studies of the role of JC virus, and to a lesser extent BK virus, in human infections and disease. Much of the work will be concentrated on the epidemiology of JC virus and BK virus and on JC virus in progressive multifocal leukoencephalopathy. 3. Study of the oncogenicity of JC virus, particularly in primates.